Feasibility study of municipal wastewater removal synchronized with electricity generation via solar-driven photocatalytic fuel cell with Bi2WO6/ZnO nanorods array photoanode

The reclamation of energy from municipal wastewater treatment process is highly demanded and could resolve the two most formidable dilemmas of water pollution and energy crisis nowadays. In this study, a photocatalytic fuel cell (PFC) utilizing a Z-scheme heterojunction Bi2WO6/ZnO nanorod arrays (NRAs) photoanode was employed for efficient municipal wastewater treatment and electricity generation simultaneously under sunlight irradiation. Various characterization techniques, including energy dispersive X-ray (EDX), field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), transient photoresponse (TPR), and linear sweep voltammetry (LSV) were used to analyze the physical, chemical and photoelectrochemical characteristics of the as-synthesized photoanode. The results indicated that the Z-scheme heterojunction Bi2WO6/ZnO NRAs exhibited the excellent photocatalytic performance under sunlight irradiation as compared to pristine ZnO NRAs. Ergo, the PFC system achieved complete removal of COD and produced 3.30 μW cm−2, 37.10 μA cm−2 and 563 mV of maximum power density (Pmax ), short-current density (Jsc) and open-circuit voltage (Voc) within 4 h of sunlight irradiation, respectively. The boosted photoactivity was ascribed to the successful formation of the Z-scheme hybridization interface betwixt the Bi2WO6 and ZnO NRAs, that not only enhanced the visible light adsorption of ZnO NRAs, concomitantly significantly accelerated the spatial charge separation and restrained the electron-hole pair recombination.

Study the Effect of the Heat Treatment on the Photoelectrochemical Performance of Binary Heterostructured Photoanode Ag2S/ ZnO Nanorod Arrays in Photoelectrochemical Cells

Heterostructured semiconductors are considered one of the most significant candidates for photoelectrochemical cells (PECs) water splitting because of their visible photovoltaic features. Hence, this study displayed the synthesis of Ag2S NPs/ZnO nanorods arrays (NRAs) as a function of annealing temperature in the range between 100 °C and 500 °C. The heterostructured photoanode was fabricated through two- simple steps synthesis; the first one was hydrothermal method (HT) and the second one successive ionic layer adsorption and reaction (SILAR) method. Structural morphology characteristics, chemical conformation and properties of synthesized nanostructure were studied via different characterization techniques such as field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), HR-TEM and EDX, correspondingly. The XRD results showed that the hexagonal phase of ZnO NRAs combined successfully with monoclinicAg2S nanoparticles. The optical properties throughout absorbance spectra disclosed that with increasing the annealing temperature, the absorbance edges shifted toward extended wavelength indicating considerable enhancement in the optical properties upon the heat -treatment. Additionally, Ag2S nanoparticles/ZnO NRAs was employed as a working photoanode in photoelectrochemical cell consists of three-electrodes configuration. The result showed an important improvement in the performance of photoelectrochemical cell. It was observed that Ag2S/ZnO NRAs upon annealing at 400 °C showed an impressive photocurrent density, photoconversion efficiency of 2.73 mA/cm2 and 2.33%, respectively by achieving ~8 times higher compared to ZnO NRAs (0.337 mA/cm2). Such this enhancement was attributed to the morphological structure improvement, crystallinity and optical properties enhancement of the heterostructured photoanode after the conducting annealing process.

Surface lattice reconstruction enhanced the photoresponse performance of a self-powered ZnO nanorod arrays/Si heterojunction photodetector

Surface lattice reconstruction enhanced the photoresponse performance of a self-powered ZnO NRAs/Si heterojunction UV-vis-NIR broadband photodetector.

Synthesis of Binary Bi2S3/ZnO Nanorod Array Heterostructure and Their Photoelectrochemical Performance

One of the most effective strategies to improve the photoconversion efficiency in the photoelectrochemical cell is by using an assembly of heterostructures. To do so, a simple and inexpensive method, that is successive ionic layer adsorption and reaction (SILAR), is used to deposit the narrow band gap energy semiconductor Bi2S3 on ZnO nanorod arrays (NRAs) at different SILAR cycles. The obtained binary heterostructure thin films were characterized by using X-ray diffraction (XRD), UV-Vis Spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and linear sweep voltammogram (LSV) to prove the crystal structure, optical properties, band gap energy, morphological structure, composition of elements, and electrical properties. The XRD revealed that ZnO NRAs possessed a single wurtzite crystal structure while Bi2S3 possessed an orthorhombic crystal structure. The as-fabricated Bi2S3/ZnO heterostructure exhibited enhanced visible light absorption and charge separation efficiency of photoinduced electron-hole pairs. The band gap energy of binary heterostructure Bi2S3/ZnO NRAs is 3.11, 3.00, 2.33, 1.96, and 1.89 eV at 3, 5, 7, 9, and 11 SILAR cycles, respectively, confirming the substantial improvement of ZnO NRA optical properties. The highest photocurrent density has been achieved by 1.92 mA/cm2 of Bi2S3/ZnO NRAs fabricated at 7 cycles, exhibiting sixfold enhancement compared to that of intrinsic ZnO NRAs (0.336 mA/cm2). This impressive enhancement was ascribed to the significant improvement in morphological structure, crystallinity, and optical properties of heterostructure photoanodes. Significant improvement was achieved in the photoelectrochemical cell (PEC) performance attributed to the fast separation, low recombination rate, and low impedance of the photoinduced electron-hole pairs as shown throughout the electrochemical impedance spectra.

Bismuth oxysulfide modified ZnO nanorod arrays as an efficient electron transport layer for inverted polymer solar cells

Vertically aligned zinc oxide nanorod arrays (ZnO NRAs) are expected to provide a direct and stable electron transport pathway in polymer solar cells (PSCs) so as to enhance charge carrier collection and transport.

MEH-PPV and PCBM Solution Concentration Dependence of Inverted-Type Organic Solar Cells Based on Eosin-Y-Coated ZnO Nanorod Arrays

The influence of polymer solution concentration on the performance of chlorobenzene- (CB-) and chloroform- (CF-) based inverted-type organic solar cells has been investigated. The organic photoactive layers consisted of poly(2-methoxy-5-(2-ethyl hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and (6,6)-phenyl C61butyric acid methyl ester (PCBM) were spin coated from CF with concentrations of 4, 6, and 8 mg/mL and from CB with concentrations of 6, 8, and 10 mg/mL onto Eosin-Y-coated ZnO nanorod arrays (NRAs). Fluorine doped tin oxide (FTO) and silver (Ag) were used as electron collecting electrode and hole collecting electrode, respectively. Experimental results showed that the short circuit current density and power conversion efficiency increased with decrease of solution concentration for both CB and CF devices, which could be attributed to reducing charge recombination in thinner photoactive layer and larger contact area between the rougher photoactive layer and Ag contact. However, the open circuit voltage decreased with decreasing solution concentration due to increase of leakage current from ZnO NRAs to Ag as the ZnO NRAs were not fully covered by the polymer blend. The highest power conversion efficiencies of0.54±0.10% and0.87±0.15% were achieved at the respective lowest solution concentrations of CB and CF.

ZnO/Al2O3 Core-shell Nanorod Arrays: Processing, Structural Characterization, and Luminescent Property

ABSTRACTWe reported the aqueous chemical method to fabricate the well-aligned ZnO/Al2O3 core-shell nanorod arrays (NRAs). The shell is composed of α-Al2O3 nanocrystals in amorphous Al2O3 layers. The photoluminescence (PL) measurements showed that the enhancement of near-band-edge emission in ZnO NRAs arrays due to the addition of Al2O3 shell was observed. The Al2O3 shell layer resulting in flatband effect near ZnO surface leads to a stronger overlap of the wavefunctions of electrons and holes in the ZnO core, further enhancing the NBE emission.

Electrical transport properties of size-tuned ZnO nanorods

Size-tuned ZnO nanorod arrays (NRAs), aligned well vertically and laterally, were synthesized by catalyst-free, metalorganic chemical vapor deposition on GaN-buffered Al2O3 (0001) substrates by adjusting the O/Zn precursor ratio in the reactor. Their electrical transport properties were investigated using field effect transistors based on individual ZnO nanorods. We find that the carrier concentrations and mobilities in the nanorods are not very sensitive to the change of the precursor ratio. This suggests that altering the precursor ratio is a way of fabricating size-tuned ZnO NRAs with quite consistent electrical properties.